The state of the art already describes the use of discarded tyres in concrete. Indeed, the requirement to search alternative uses to the rubber derived from discarded tyres (PFU), met the need of improving some characteristics of the mixtures of concrete. Indeed, according to the applications to which it is destined, the concrete shall have a low specific weight, a high strength and resistance to impact. The concrete as such, although it is the most used building material, not always satisfies all these requisites contemporaneously.
It has been thus developed in the state of the art the use of rubber particles derived from PFU as constituent in the concrete, with use of the product thus obtained in the achievement of cement sound absorbing products for road applications. More recently, the particles of recycled rubber have been used in the mixtures of concrete, still in replacement of aggregates based on inert materials, to obtain a light concrete.
In particular, within the technical literature, under the wording “Rubber Concrete” (concrete with rubber) or “Rubber Modified Concrete” (concrete modified with rubber) it is usual to indicate a mixture composed of ordinary concrete (Portland cement), natural aggregates and rubber from discarded tyres. Under the wording “Rubber mortar” it is intended to indicate the mixture of cement mortar with rubber.
The rubber used for such applications derives from post-consuming tyres of vehicles or trucks subjected to treatments of mechanical grinding or to cryogenic processes. Moreover, according to applications and performances required to the end-product, the rubber has been used “as such” or in some cases it has been previously treated, removing the textile component therefrom or pulling out the steel fibres. In other cases, the surface of rubber has been subjected to some pre-treatments to reinforce the adhesion between cement paste and rubber, achieving a marked improvement of some of the final properties of concrete. An example of said pre-treatment is a surface treatment of rubber with sodium hydroxide, which increases the adhesion between particles of rubber and cement matrix, translating thus in a substantial improvement of wear resistance and bending resistance.
In general, rubber aggregates have been used only as partial substitution of natural aggregates inside the mixture of concrete.
According to the state of the art, the addition of particles of rubber of discarded tyres leads to a reduction of physical and mechanical properties of the starting concrete, but at the same time leads to a great capability of plastic energy absorption. The decrease of mechanical properties is proportional to the increase of the fraction by volume of rubber according to a non-linear relationship.
Through addition of rubber, the concrete becomes relatively ductile and, if subjected to loading, behaves as an elastic structure.
Moreover, concrete with particles of rubber (in substitution of an amount between 10% and 30% by weight of the aggregate in inert materials) present coefficients of thermal conductivity and sound absorption greater than those of a traditional concrete.
Basing on the above highlighted properties, the concrete with recycled rubber can be used in architectural applications, in road paving wherein high mechanical resistances are not required, in panels requiring a low specific weight, in elements for construction and Jersey barriers subjected to impacts, in sound barriers (sound absorbing) and in construction of railroads to fasten the rails to the ground.
Examples of such applications are disclosed in patent applications WO2009035743, WO2000027774 and RU-A-2353603, relating to cement mixtures, rubber particles and natural aggregates, respectively, for general uses for concrete with latex, cement panels and mortars, for applications of radiation shielding and for uses as perimeter walls with blocks made of light concrete.
The need to seek alternative uses to the rubber deriving from discarded tyres (PFU) met nowadays with the need to improve some characteristics of the mixtures of concrete in order to make it a material capable to adsorb the energy developed by dynamic actions (impacts and vibrations).
It arose thus the interest in the achievement of screeds based on concrete containing aggregates in PFU rubber.
The conventional screed, pursuant to UNI EN 13813, is that horizontal construction element adopted, for example, to level a surface, making it perfectly flat, for distributing the load of the overlying elements and/or for receiving the final paving. The screed is a construction element with a variable thickness depending on the type of environment and purpose to which it is destined (for example inside a building it may have a thickness from 4 to 20 cm).
The conventional screed is usually obtained through the use of at least three materials used in appropriate amounts: cement, inert materials (sand and/or grit, for example) and water. Possibly, super-fluidifiers or aerating additives may be added. The dosage of the various elements varies according to the type of environment and to the destination of the screed (internal or external, for industrial or civil purposes). Much often other components are present, such as polystyrene, used to lighten the screed, or quartz, used to make the screed smoother and stronger. A screed laid adhering to a load-bearing substrate (for example a loft), on a desolidarisation layer (for example barrier to vapour) or on a layer of thermal and/or acoustic insulation, is defined respectively as “adherent”, “desolidarised” or “floating”. A screed may also incorporate a floor heating/cooling system and, in that case, it is defined “radiant”.
The obtainment of the screed shall thus ensure mainly:                the achievement of a support suitable for the laying of the planned pavement;        that the laying occurs in the required timeframe;        that the lasting of the construction work under the various operating conditions (inside or outside, in paves for civil, commercial or industrial use, etc.) is not jeopardized.        
The aim of the present invention is therefore that of proposing a screed capable to meet at the same time the above said thermal/mechanical features, ensuring also a noise reduction and adsorption of vibrational energy, in particular a reduction of the noise from footsteps, overcoming thus the drawbacks of the products according to the prior art.
A further aim of the present invention is the use of said screed in applications requiring a reduced noise from footsteps.